The present disclosure relates to a hydraulic control device of an automatic transmission including a plurality of engagement elements that is mounted, for example, on a vehicle, and more in detail, to a hydraulic control device of an automatic transmission that can cut off the supply pressure for a predetermined one of a plurality of predetermined engagement elements such that the engagement elements are prevented from simultaneously being engaged.
Conventionally, in a stepped automatic transmission mounted, for example, on a vehicle, a hydraulic control device controls engagement states of a plurality of engagement elements (clutches and brakes) to establish a transmission path in a speed change mechanism at each shift speed, so that multi-speed transmission is achieved. To avoid a tie-up in which engagement elements that should not normally be simultaneously engaged are engaged in the speed change mechanism, a hydraulic control device as described above is known which includes a hydraulic circuit that is provided with a plurality of cut-off valves for the respective engagement elements and does not supply hydraulic pressure under certain conditions (refer to Japanese Patent Application Publication No. 2009-52618). An automatic transmission of Japanese Patent Application Publication No. 2009-52618 includes two clutches and three brakes, and the two clutches and two of the brakes are each provided with a cut-off valve, thus, in total, four cut-off valves.
In recent years, an automatic transmission has been developed which includes four clutches and two brakes and is capable of establishing ten forward speeds by simultaneously engaging three friction engagement elements (refer to U.S. Pat. No. 8,096,915).